1. Field of the Invention
The present invention relates to an attitude angle detecting apparatus for detecting changes in an attitude angle of an artificial satellite in a wide band with ground offline processing at a high precision and a method thereof.
2. Description of the Prior Art
FIG. 5 is a configuration diagram showing an example of a conventional attitude determining apparatus. Reference numeral 101 represents an attitude angle calibration sensor, reference numeral 102 represents an angular velocity sensor, reference numeral 3 represents a sequential Kalman filter computing device, reference numeral 104 represents an attitude angle calibration sensor detection signal, reference numeral 105 represents an angular velocity sensor detection signal and reference numeral 106 represents an attitude angle determining signal.
Referring to FIG. 5, an angular velocity sensor detection signal 105 detected by the angular velocity sensor 102 and an attitude angle calibration sensor detection signal 104 detected by the attitude angle calibration sensor 101 are inputted to the sequential Kalman filter computing device 3 so as to generate an attitude angle determining signal 106 which is an attitude angle estimation value of the artificial satellite. The sequential Kalman filter computing device 3 realizes noise characteristics of the angular velocity sensor 102 (for example, gyroscope) and the attitude angle calibration sensor 101 (for example, star tracker (STT) which is a fixed star sensor) which are loaded on the artificial satellite in the form of a probability model. With that model, noises contained in the angular velocity sensor detection signal 105 and the attitude angle calibration sensor detection signal 104 are estimated and removed so as to generate the attitude angle determining signal 106 of the artificial satellite at a high precision.
Because the conventional attitude determining apparatus as shown in FIG. 5 can be made with a relatively simple structure, it has been originally developed as a processing (i.e., real-time processing) system on board. However, if the angular velocity sensor detection signal 105 and the attitude angle calibration sensor detection signal 104 can be extracted from telemetry data received on ground as time-series data, they can be applied easily to offline processing system. For this reason, the conventional attitude determining apparatus as shown in FIG. 5 has been widely used as an apparatus common among an onboard processing system and a ground processing system.
However, although the attitude angle calibration sensor 101 such as STT generally has an excellent measuring accuracy, its measuring cycle is 10 times longer than the angular velocity sensor 102. Thus, even if the measuring cycle of the angular velocity sensor 102 is improved, there is a limit of detection in frequency band due to an influence of waste time. Although the changes of the artificial satellite attitude can be detected up to high frequency band in case only the angular velocity sensor 102 is used. However, in this case, an influence of noise contained in the angular velocity sensor detection signal 105 is increased, so that the accuracy of the attitude angle determining signal 106 generated by the sequential Kalman filter computing device 3 is deteriorated considerably.
In order to overcome the aforementioned disadvantages, the present invention has been made and accordingly, has an object to provide an apparatus for detecting an attitude of an artificial satellite in wide-band capable of detecting an artificial satellite attitude in wide band at a high precision.
To achieve the above object, according to a first aspect of the present invention, there is provided an apparatus for detecting an attitude of an artificial satellite comprising: telemetry data memory for storing and holding data from the artificial satellite; an attitude angle calibration sensor data extracting device for extracting an attitude angle calibration sensor detection signal from said telemetry data memory as time-series data; an angular velocity sensor data extracting device for extracting an angular velocity sensor detection signal from the telemetry data memory as time-series data; a sequential Kalman filter computation device for generating an attitude angle determination signal from the attitude angle calibration sensor detection signal and the angular velocity sensor detection signal; a low-pass filter computation device for generating a low frequency attitude detection signal from the attitude angle determination signal; an interpolation processing computation device for generating a low frequency attitude interpolation signal from the low frequency attitude detection signal; a high-frequency attitude angle sensor data extracting device for extracting a high-frequency attitude angle sensor detection signal from the telemetry data memory as time-series data; a band pass filter for generating a high-frequency attitude detection signal from the high-frequency attitude angle sensor detection signal; and an attitude data generator for generating a high-precision attitude detection signal from the low-frequency attitude interpolation signal and the high-frequency attitude angle detection signal.
Under the above-described structure, it is possible to employ a star tracker (STT) as the attitude angle calibration sensor, a gyroscope as the angular velocity sensor, and an angle displacement sensor (ADS) using liquid as the high-frequency attitude angle sensor.
According to a second aspect of the present invention, there is provided the apparatus for detecting an attitude of an artificial satellite according to the first aspect, wherein the interpolation processing computation device generates the low-frequency attitude interpolation signal by interpolating the low-frequency attitude detection signal by cubic spline interpolation.
According to a third aspect of the present invention, there is provided the apparatus for detecting an attitude of an artificial satellite according to the first aspect, wherein the interpolation processing computation device generates the low-frequency attitude interpolation signal by carrying out linear approximate interpolation on the low-frequency attitude detection signal, and the attitude data generator generates the high-precision attitude detection signal by interpolating the high-frequency attitude angle detection signal using an interpolation value of the low-frequency attitude detection signal outputted from the interpolation processing computation device.